The present invention relates to a hydrodynamic bearing to be used for an apparatus having a rotating mechanism, such as a disk recording/reproducing apparatus for recording and/or reproducing data while rotating a disk at a high speed.
Recently, in a disk recording/reproducing apparatus for recording and/or reproducing data while rotating the disk, the memory size greatly increases and the data transfer speed becomes very high. Therefore, it becomes necessary to provide mechanism for achieving a high speed and high precision rotation force in a rotating mechanism incorporated in such disk recording/reproducing apparatus. Accordingly, a high-speed rotatable hydrodynamic bearing which is constituted so as to support both ends of a main shaft, such as for example described in U.S. Pat. No. 5,504,637, is employed in a rotating mechanism of a disk recording/reproducing apparatus.
A conventional hydrodynamic bearing described in U.S. Pat. No. 5,504,637 is explained hereunder as an example of a prior art with reference to FIG. 10.
FIG. 10 is a cross-sectional view showing a constitution in the vicinity of a main shaft in a conventional hydrodynamic bearing. In FIG. 10, an end portion (lower end portion in the drawing) of a fixed shaft 22 that is the main shaft is fixed to a base member 21. A flange member 23 is fixed in the proximity of the other end portion of the fixed shaft 22. A sleeve 24 and a rotor hub 25 are formed in one integral and is provided rotatable around the fixed shaft 22. An outer circumferential end face of the flange member 23 is disposed inside of a stepped recess 25A formed on the rotor hub 25. A thrust plate 26 is placed so as to confront the upper face of the flange member 23. The thrust plate 26 is fixed to the rotor hub 25 so that the thrust plate 26 can rotate around the fixed shaft 22. Two sets of herringbone-shaped radial hydrodynamic pressure grooves 24A and 24B are formed on the outer circumferential surface of the fixed shaft 22. And, herringbone-shaped thrust hydrodynamic pressure grooves 23A are formed on the upper face of the flange member 23, which is confronting the thrust plate 26. Further on the lower face of the flange member 23, thrust hydrodynamic pressure grooves 23B are provided. The radial hydrodynamic pressure grooves 24A and 24B, as well as thrust hydrodynamic pressure grooves 23A and 23B are filled with lubricant 27.
A rotor magnet 28 is attached to the rotor hub 25 formed in one unified body with the sleeve 24. And, a motor stator 29 is attached to the base member 21 so as to confront the rotor magnet 28.
In FIG. 10, a space shown by reference numeral 22A is a ventilating path, which has a function for discharging air received in a clearance xe2x80x9cHxe2x80x9d in the proximity of the outer circumferential portion of the flange member 23. A space shown by numeral 24D in FIG. 10 is also a ventilating path for discharging air received in a clearance xe2x80x9cJxe2x80x9d in the proximity of the lower inner circumferential portion of the flange member 23.
Operations of the conventional hydrodynamic bearing constituted as above are described with reference to FIG. 10.
When power is supplied to the motor stator 29 so that a rotative magnetic field is generated, the rotor magnet 28 starts to rotate along with the rotating members including the rotor hub 25, sleeve 24 and the thrust plate 26, etc. Concurrently, the herringbone-shaped radial hydrodynamic pressure grooves 24A and 24B collect the lubricant toward the central portion thereof. As a result a pressure is generated in a clearance between the outer circumferential surface of the fixed shaft 22 and the inner circumferential surface 24C of the sleeve 24, because the lubricant is squeezed into this clearance by pumping effect. Likewise, a pressure is generated around the herringbone-shaped thrust hydrodynamic pressure grooves 23A and 23B, by the pumping effect to squeeze the lubricant.
By such pressure generated by the lubricant 27, the rotating members around the fixed shaft 22 rotate perfectly in non-contact state with the fixed shaft 22. Consequently disks that are the recording mediums (omitted in the drawing) attached to the rotor hub 25 are driven to rotate together with the sleeve 24. As a result, electric signal is recorded on or reproduced from the disk through a head (omitted in the drawing). Detailed description of operations for recording and reproducing to be performed here is omitted since they are similar to known recording and reproducing processes of a hard disk driving apparatus (HDD).
The conventional hydrodynamic bearing constituted as above has the following disadvantages.
As shown in FIG. 10, the lubricant 27 is applied to the thrust hydrodynamic pressure grooves 23A as well as in the clearance xe2x80x9cHxe2x80x9d between the outer circumferential end face of the flange member 23 and the inner circumferential surface of the stepped recess 25A. During the hydrodynamic bearing is at rest, the lubricant 27 contained in the clearance xe2x80x9cHxe2x80x9d moves toward a clearance xe2x80x9cGxe2x80x9d which is narrower than the clearance xe2x80x9cHxe2x80x9d, due to capillary action. The clearance xe2x80x9cGxe2x80x9d is located between the inner circumferential surface of the thrust plate 26 and the outer circumferential surface of the fixed shaft 22. The lubricant 27 which has moved into the clearance xe2x80x9cGxe2x80x9d becomes in a visible state to stand up above the end of the clearance xe2x80x9cGxe2x80x9d, with the lapse of time. When power is supplied to the motor stator 29 and the rotor magnet 28 starts to rotate with the sleeve 24, rotor hub 25 and thrust plate 26 under such a state. At the instant, the lubricant 27 in the clearance xe2x80x9cGxe2x80x9d instantly became lubricant drops 27a and 27b and splashes out of the hydrodynamic bearing as a result of centrifugal force. In FIG. 10, a mark xe2x80x9cRHxe2x80x9d shows a distance in a radial direction of the clearance xe2x80x9cHxe2x80x9d between the outer circumferential end face of the flange member 23 and the inner circumferential surface of the stepped recess 25A. Also a mark xe2x80x9cRGxe2x80x9d shows a distance in a radial direction of the clearance xe2x80x9cGxe2x80x9d between the inner circumferential surface of the thrust plate 26 and the outer circumferential surface of the fixed shaft 22. As shown in FIG. 10, the distance xe2x80x9cRFxe2x80x9d was greater than the distance xe2x80x9cRGxe2x80x9d (i.e., RH greater than RG) in a conventional hydrodynamic bearing.
In addition, in the conventional hydrodynamic bearing, the lubricant 27 is applied to the thrust hydrodynamic pressure grooves 23A formed on the flange member 23 as well as to clearances xe2x80x9cKxe2x80x9d and xe2x80x9cLxe2x80x9d between the outer circumferential surface of the fixed shaft 22 and the inner circumferential surface of the sleeve 24. Once the rotating members such as the rotor magnet 28, sleeve 24, rotor hub 25 and thrust plate 26, etc. start rotating under such state, the lubricant 27 in the clearance xe2x80x9cLxe2x80x9d turns into overflow lubricant as a result of centrifugal force and starts to flow out (downward in FIG. 10) of the hydrodynamic bearing. In FIG. 10, a mark xe2x80x9cRKxe2x80x9d shows a distance in a radial direction of the clearance xe2x80x9cKxe2x80x9d between the outer circumferential surface of the fixed shaft 22 and the inner circumferential surface of the sleeve 24, and a mark xe2x80x9cRLxe2x80x9d shows a distance in a radial direction of the clearance xe2x80x9cLxe2x80x9d. As shown in FIG. 10, the distance xe2x80x9cRKxe2x80x9d was greater than the distance xe2x80x9cRLxe2x80x9d (i.e., RK greater than RL) in the conventional hydrodynamic bearing.
As described above, the conventional hydrodynamic bearing has the disadvantage that the lubricant 27 flows out of the clearances xe2x80x9cGxe2x80x9d or xe2x80x9cLxe2x80x9d, amount of the lubricant 27 decreases, and therefore the lubricant 27 may finally become no longer effective. In addition, since the lubricant 27 splashes out of the apparatus, the lubricant 27 may adhere to other apparatus, thus causing unfavorable effect.
Briefly stated, in one aspect, the present invention is a hydrodynamic bearing comprising a fixed shaft having one end fixed to a base member. A disk-shaped flange member is disposed in the proximity of the other end of said fixed shaft and through a hole of which said fixed shaft is penetrating. Rotating members are disposed so as to enclose said flange member and through which said fixed shaft is penetrating. A motor has a rotor unit attached to one of said rotating members. A stator unit is fixed to said base member so as to confront said rotor unit, wherein at least either of the confronting faces of one of said rotating members and said fixed shaft is provided with radial hydrodynamic pressure grooves. At least either of the confronting faces of said flange member and one of said rotating members is provided with thrust hydrodynamic pressure grooves. Said radial hydrodynamic pressure grooves and said thrust hydrodynamic pressure grooves are filled with lubricant and relations of d1 greater than d2 and 0.2 mmxe2x89xa6d1xe2x88x92d2xe2x89xa60.8 mm are satisfied. xe2x80x9cd1xe2x80x9d is a diameter of a central portion where said radial hydrodynamic pressure grooves of said fixed shaft are formed or said radial hydrodynamic pressure grooves of said rotating member are confronted. xe2x80x9cd2xe2x80x9d is a diameter of the other end portion of said fixed shaft beyond said flange member. A clearance is secured between an outer circumferential surface of the other end portion having a diameter of xe2x80x9cd2xe2x80x9d and an inner circumferential surface of one of said rotating members confronting said outer circumferential surface.
In another aspect, the present invention is a hydrodynamic bearing comprising a fixed shaft with one end fixed to a base member. A disk-shaped flange member is disposed in the proximity of the other end of said fixed shaft and through a hole of which said fixed shaft is penetrating. Rotating members are disposed so as to enclose said flange member and through which said fixed shaft is penetrating. A motor has a rotor unit attached to one of said rotating members. A stator unit is fixed to said base member so as to confront said rotor unit, wherein at least either of the confronting faces of one of said rotating members and said fixed shaft is provided with radial hydrodynamic pressure grooves. At least either of the confronting faces of said flange member and one of said rotating members is provided with thrust hydrodynamic pressure grooves. Said radial hydrodynamic pressure grooves and said thrust hydrodynamic pressure grooves are filled with lubricant and relations of RA greater than RB, 0.1 mmxe2x89xa6RAxe2x89xa60.8 mm and 0.05 mmxe2x89xa6RBxe2x89xa60.5 mm are satisfied. xe2x80x9cRAxe2x80x9d is a distance in a radial direction of a clearance between an outer circumferential surface of the other end portion of said fixed shaft beyond said flange member and an inner circumferential surface of one of said rotating members confronting said outer circumferential surface of said other end portion. xe2x80x9cRBxe2x80x9d is a distance in a radial direction of a clearance between an outer circumferential end face of said flange member and an inner circumferential surface of one of said rotating members confronting said outer circumferential end face.